docs: def stats(self):
          """
          Return statistics calculated overall features in the container.
  
          Note:
              The feature container has to be opened in advance.
  
          Returns:
              DataStats: Statistics overall data points of all features.
          """
          self.raise_error_if_not_open()
  
          per_key_stats = self.stats_per_key()
  
          return stats.DataStats.concatenate(per_key_stats.values())